1. Field of the Invention
The invention is in the field of syringes employed in the medical field, particularly those used for injecting fluids or for aspirating fluids or tissue under the influence of a vacuum, and most particularly those which employ a locking device.
2. The Related Technology
Syringes are used in the medical field both for injecting medications into a patient, for aspirating fluids and tissue from a patient, and for injecting or aspirating fluids in connection with other types of apparatus, as for example when preparation the balloon of a dilation catheter. In most such applications, whether the syringe is being used for injecting or aspirating, a vacuum is effected in the barrel of the syringe, although the reasons for the vacuum are quite different.
In the situation wherein the syringe is being used for injection will be described first. In this situation the barrel of the syringe is partially filled with a medicinal fluid and a hypodermic needle or equivalent is attached to the distal end of the barrel. The hypodermic needle is then inserted into the patient, with the intent of having the point of the needle inserted into a vein. However, it sometimes happens that the point of the needle is not within a vein, but, unknown to the doctor or nurse, is positioned within subcutaneous tissue. If the plunger of the syringe were then pushed into the barrel of the syringe the fluid would be injected into a wrong location, with perhaps disastrous results. In order to assure the proper positioning of the needle the practitioner normally follows the following procedure. The practitioner first injects the tip of the needle deliberately into subcutaneous tissue, and then withdraws the plunger partially from the barrel. This creates a vacuum in the barrel of the plunger distal to the piston head. The practitioner then follows through so as to inject the tip of the needle into the desired vein. If the needle tip is truly within the vein then a small amount o blood will be sucked into the barrel under the influence of the vacuum. Since the barrel wall is transparent the practitioner can see the blood, and then is assured that the vein has been found, and injection can proceed.
In the second situation noted above the practitioner is interested not in injecting a fluid into the patient but in aspirating fluid, or even tissue, from the patient. In this situation the practitioner creates a vacuum in the syringe as before and then follows through so as to insert the tip of the needle into the desired vein or tissue. The vacuum then causes fluid or tissue to be aspirated.
In the third situation described above where the syringe is used for injecting or aspirating fluids in connection with other types of apparatus, as in the case when the balloon of the dilation catheter is prepared, the syringe is connected to the catheter and tubing so that by withdrawing the syringe plunger, fluid is withdrawn from the balloon of the dilation catheter during the setup procedure. As in the other two situations mentioned above, when this is done a relatively strong vacuum is created within the barrel of the syringe which tends to exert a force on the syringe plunger that would otherwise pull the syringe plunger back into the barrel of the syringe unless the syringe plunger is restrained by grasping it tightly and holding it. Thus, the creation of a vacuum in the syringe under any one of the three kinds of situations described above tends to pull the plunger back into the syringe barrel unless some means is employed to prevent it.
With some syringes this means is supplied by the practitioner holding onto the shank of the plunger so as to prevent it from being drawn into the barrel of the syringe. However, this is awkward, and sometimes necessitates the use of two hands. Therefore, many syringes employ some form of a locking device whereby the practitioner can lock the plunger in place once the vacuum has been effected. However, these syringes almost universally require that the plunger, or some other member, be rotated to effect the locking function and/or the unlocking function. Alternatively, or additionally, they require that the plunger and the barrel of the syringe be oriented with respect to each other in some requisite orientation. These requirements impose a restriction on the part of the practitioner which it would be desirable not to have.
Furthermore, the locking devices of existing syringes almost universally require extensive modifications of the barrel, and/or the plunger, thus making it impossible to perform simple, relatively inexpensive, modifications to existing syringes in order to add a locking device.
Additionally, the locking devices oftentimes comprise corners or teeth that tend to catch on the surgical gloves used by the practitioner. This, of course, is quite objectionable, even dangerous. Additionally, some syringes tend to draw in a portion of the gloves of the practitioner as the plunger is drawn into the barrel. This is also annoying as the practitioner must disengage such gloves, a practice which may require two hands, perhaps even the assistance of a second person.